The present invention relates to mineral recovery, and more particularly to bitumen and viscous crude oil recovery by use of hydraulic mining techniques.
With the world demand for petroleum products rising to unprecedented levels and the known accumulated oil reservoir supplies being rapidly depleted, attention has been directed to means for recovering high viscosity crude oil from subterranean mineral deposits such as tar sands or bitumen sands which are known to contain substantial crude oil reserves. Due to the high viscosity of the crude oil carried in the tar sands, and the low reservoir pressures generally found in these shallow oil formations, conventional petroleum recovery techniques are rendered ineffective by various environmental and regulatory restrictions and prove to be generally unsuitable for extracting the crude oil from the shallow formation sand deposits. Additionally, the extraction of such viscous crude oil through steam injection proves ineffective in many of the shallow oil formations.
Heretofore, the recovery of such high viscosity crude oil was typically accomplished by either strip mining, wherein the tar-like sand deposits are removed by mechanical means and transported to the surface for subsequent separation of the crude oil from the same or in-situ separation, wherein the crude oil is separated in place from the tar-like sands by use of thermal processes to reduce the viscous properties of the crude oil, and subsequently pumped to the surface. The use of the strip mining and in-situ separation methods have been found to be extremely cost prohibitive, and often unable to meet environmental and other regulatory requirements. As such, the mining of tar sands has remained relatively dormant.
Very recently, hydraulic mining techniques have been developed which have proven to be more economical in the recovery of the high viscosity crude oil and generally compatible with the various environmental and regulatory requirements. Basically, such hydraulic mining techniques utilize a high velocity liquid which is discharged into the tar sand formation, to dislodge the viscous crude oil and sand particles therefrom. The freed viscous crude oil and oil encapsulated sand particles mix with the high velocity liquid discharge forming an aqueous slurry which may be pumped, as by way of a hydraulic jet pump, to the surface and subsequently processed by conventional surface systems to yield a separation of the viscous crude oil from the sand particles. Techniques such as steam cycle, steam drive, and in-situ combustion, heretofore used to recover viscous crude oil, require significant amounts of crude oil to be used as fuel to provide energy for the process. As such, the recent hydraulic mining techniques drastically increase recovery efficiency and save valuable resources. Examples of such recent hydraulic mining tools are U.S. Pat. No. 3,439,953, issued to Pfefferle, U.S. Pat. No. 3,951,457, issued to Redford, and my co-pending patent application, Ser. No. 053,029, filed June 28, 1979, entitled DOWN HOLE PUMP WITH BOTTOM RECEPTOR, the disclosures of which are expressly incorporated herein by reference. Although these recently developed hydraulic mining tools have proven to be more cost effective in the recovery of viscous crude oil from tar sands than the previous strip mining and in-situ separation mining methods, they have possessed certain inherent deficiencies which have detracted from their overall efficiency during operation.
These deficiencies have focused upon the tendency of the jet pump, utilized to lift the aqueous slurry upward to the surface, to become clogged with rocks, clay, formation debris, or other obstructions during operation, the inability of the mining tools to penetrate large rock formations and rock particles which accumulate under the mining tools during operation thereby restricting the lowering of the mining tool within the tar sands, and the typical failure of the mining tools to include any means to ensure that a constant slurry/tar sand supply be introduced into the jet pump.
In relation to the tendency for the jet pump nozzle to become obstructed during operation, it will be recognized that the viscous crude oil sand formations are often laced with various hard rock particles or formations which, during the mining process, migrate in the aqueous slurry toward the jet pump venturi throat. If the rock particle size is greater than the throat of the venturi, the particles become lodged therein, substantially reducing, if not completely closing off the slurry inlet to the jet pump. Although this problem has been recognized with more recent mining tool designs incorporating screen meshes over the jet pump venturi throat, such screens are subject to being torn during operation and further are often themselves subject to becoming clogged by the high viscosity crude oil released from the tar-like sand formations and restricted by the accumulation of mined rock particles adjacent the venturi pump inlet.
Additionally, most hydraulic mining tools have utilized a conical-shaped cutting auger at their lower-most end which, during rotation of the mining tool, permits the tool to be lowered deeper into the tar sand formation. Although effective in relatively consistent soft formations, such conical augers are incapable of penetrating hard rock formations which, as previously mentioned, are commonly interspersed or laced within the tar-like sand, and fail to remove large rock cuttings from the mining hole. As such, upon confronting a hard rock formation, these conical-shaped augers merely bounce thereon thereby preventing the tool from being lowered deeper into the tar-like sand formations. With the vertical depth of the mining tool limited, the amount of available slurry and mined material surrounding the mining tool is reduced, with the attendant reduction in slurry recovery.
Further, the existing hydraulic mining tools have typically relied solely upon the natural gravity force migration of the slurry within the formation and the suction developed by the jet pump to transport the slurry into the jet pump venturi throat. This lack of any positive means to supply the slurry into the venturi throat has resulted in varying recovery efficiencies, dependent upon the varying rate of migration of the slurry within the tar sand formation.
Thus, there exists a substantial need for a hydraulic mining tool which does not become clogged during operation, can penetrate hard rock formations and clear formation debris, and includes means to supply a continuous quantity of slurry into the jet pump venturi throat.